Sloane Stephens has lost three of her four previous matches against Stefanie Vogele, her Tokyo victory five years ago her sole success amid defeats in Linz and Luxembourg in the same year and another loss at the 2008 US Open.

Shuai Zhang hopes to maintain her winning record against Rebecca Peterson, having beaten the Swede in their previous meeting, in Honolulu last year.

Veronica Cepede Royg faces Daria Gavrilova for the first time.

Lesia Tsurenko takes on Kristina Mladenovic in a rematch of last year's Acapulco final. The Ukrainian's victory last March was her fifth in sixth matches against the Frenchwoman, whose only victory over Tsurenko came in Dubai in 2016.